The present invention relates to a cylinder head gasket for internal-combustion engines including at least one disc of soft material whose pores are completely or partially enriched with an impregnatng agent which in its final stage is thermoplastic, duroplastic or elastic, the edges of the disc being bound by a flange.
Cylinder head gaskets for internal-combustion engines usually consist of a thermally stable fibrous material such as asbestos, for example, which is possibly reinforced by an embedded metal disc. Small quantities of natural or synthetic rubber are usually added to the asbestos fibers in order to provide better binding.
Cylinder head gaskets have passages for the combustion chambers, the coolant and the lubricant. At the edges of these passages the seal must be particularly tight against the hot gases from the combustion chamber, which gases are under pressure, the lubricant and the coolant, which may possibly contain anti-freeze and corrosion protection agents. A normal asbestos fiber disc enriched with binders and possibly reinforced with embedded metal discs is not satisfactory for such purposes because the porosity of the asbestos material is too high and thus its cross-sectional density is too low.
On the one hand, in order to provide a better surface seal, the edges of the passages have been provided with a bordering casing, usually of copper or iron, which may be coated with a plastic layer of aluminum or a synthetic material. The bordering casing for the combustion chamber passage generally has a U-shaped cross section with the opposing arms of the U lying on the opposing lateral planar surfaces of the gasket and the curved base of the U lying against the cylindrical surface of the passage so that all of edges of the combustion chamber passages are protected. The bordering casing for coolant, lubricant and other passages generally comprises metal discs which lie on the lateral planar surfaces of the gasket to protect the planar surfaces of the gasket, while the cylindrical surfaces of these passages are not protected by a casing. On the other hand, it is known to increase the cross-sectional density by coating or saturating the asbestos fiber layer with a synthetic material to increase the sealing performance of the gasket. According to German Pat. No. 1,072,032, a gasket is impregnated in the immediate region of the passages with impregnating agents such as solutions, dispersions, emulsions or latexes of polymerized or polymerizable substances. According to German Pat. No. 740,388 and U.S. Pat. No. 2,040,348 the saturating agent is a self-drying vegetable oil, such as linseed oil for example.
Naturally the cross-sectional density of cylinder head gaskets increases with the quantity of impregnating agent absorbed in the fiber. However, the more the fiber is saturated, the lower becomes its compressibility. If the latter becomes too low, the gasket can no longer adapt itself too well to the unevennesses of the cylinder head and of the cylinder block and part of its sealing capability is lost.
This applies particularly for the area of the gasket having a bordering casing and especially for the area of the gasket having the metal casings on opposing sides of the gasket because there the thickness of the cylinder head gasket is increased by twice the thickness of the metal. Consequently when the cylinder head gasket is installed it must be more compressible in this area to compensate for these differences in thickness.